1. Field of the Invention
The present invention relates to a vehicle rearview mirror and more particularly, to a lens for a rearview mirror combined with a liquid crystal display (LCD) monitor, which optimizes the recognition of the LCD light source.
2. Description of the Related Art
Following fast development of high technology, people can quickly obtain different information and messages from different sources. In order to let the driver obtain the latest information, automobile manufacturers install an LCD monitor in the internal rearview mirror of each car. When driving the car, the driver can obtain from the LCD monitor in the car's internal rearview mirror the desired information such as driving speed, distance with the car moving ahead or the car approaching from behind (integrated with the back sensor), and other related data.
FIG. 1 shows a lens for a rearview mirror for the above-mention purpose according to the prior art design. According to this design, the lens comprises a glass substrate 1, a coating layer 2, and a back layer 3. The coating layer 2 is evenly coated on the back surface of the glass substrate 1. The back layer 3 is covered on the coating layer 2, leaving a predefined area of the coating layer 2 in blank. Therefore, the predetermined area of the coating layer 2 that is not covered by the back layer 3 forms a transmission zone 4 for the passing of the light emitted from the LCD monitor to the outside of the rearview mirror during the operation of the LCD monitor so that the driver can see the image provided by the LCD monitor. However, there is a standard, i.e. Standard E-MARK R46, governing the reflectivity of a vehicle's internal rearview mirror, i.e., the reflectivity of the lens must be over 40% so that the driver can see clearly the image of the rear side of the car reflected by the lens of the rearview mirror to ensure a safety driving. Because the main function of the coating layer 2 is to cause a reflection of light and the function of the back layer 3 is to absorb light properly and to reduce the color difference between the reflected image and the light from the LCD monitor, the reflectivity of the coating layer 2 must be increased to about 60–70% so that the reflectivity of the lens can be maintained over 40% after the light absorbing action of the coating layer 2 and the back layer 3. However, because the transmission zone 4 cannot be covered by the back layer 3 (for enabling the light of the LCD monitor to pass), the reflectivity in the transmission zone 3 is as high as 60–70%, i.e., the transmissivity T1 of the transmission zone 4 is only about 30–40%. This low transmissivity of the transmission zone 4 will reduce the brightness of the light (information) provided by the LCD monitor. Therefore, the image reflecting intensity (reflectivity about 60–70%) in the transmission zone 4 will surpass the light intensity (transmissivity about 30–40%) of the light provided by the LCD monitor, and an illusion will be produced due to an overlay of the information provided by the LCD monitor on the reflecting image. Further, in order to protect the user's eyes against the irritation of long wavelength light, a blue glass is commonly used for the lens. However, under a high reflectivity, the long wavelength light will cause a reddish image after passing of the light from the LCD monitor through the glass substrate 1, such reddish image will irritate the user's eyes.